Patent GB-711221-A (GB)
Title: Extension mechanism for photographic cameras
IPC: G03B3/02
Filed: 1951-05-04
Abstract: 711,221. Collapsible photographic cameras. VOIGTLANDER & SOHN AKT.-GES. May 4, 1951 [May 5, 1950], No. 10519/51. Class 98(1) A photographic camera having a two-flap front cover, and an objective lens support which is sunk into the camera body in the position of rest but is moved forward out of the body into the operative position, has, on the front of the camera body or of a carrier adjustable in the camera body for focusing, extension bars constructed as single arm levers which carry or constitute the cover flaps swingably arranged on each side of the optical axis, to which bars are connected links which hold the lens support and which during outward movement of the lens support from the camera first swing the extension bars away from the optical axis and after passing a dead position again draw them inwards towards the optical axis. The support 7 for the objective lens, Fig. 6, is pivoted on each side at 22, 23 to two links 18, 19 pivoted at their other ends at 20, 21 to bars 13, 14 which in turn are pivoted at 11, 12 to a carrier 6. This carrier is mounted in the camera casing (not shown) in such a manner that it is movable towards and away from the focal plane while remaining parallel thereto, preferably by means of the range-finder adjustment. The lens support 7 may be pressed down into the carrier 6 and latched in position by known means. The lens is then covered by flaps 2, 3 fixed to bars 13, 14, the edge of the flap 3 overlying a rebate 4 or the like formed on the edge of flap 2. Springs 24, 25 coiled round pivots 20, 21 urge links 18, 19 towards bars 13, 14, and a spring 17 coiled round pivot 12 urges lever 14 away from carrier 6. The angle between links 18, 19 and bars 13, 14 is a maximum at a point where the lens support is between its retracted and extended positions, i.e. the position in which pivots 11, 12, 22, 23 are in line. From this point, springs 24, 25 tend to urge the lens support 7 either towards or away from carrier 6, according to which way the support is urged. To prevent the ends of support 7 from moving in opposite directions, levers 28, 29, pivoted together scissors-fashion at 30, are pivoted at 31, 34 to the support 7 and carrier 6, and pins 32, 35 at their free ends engage slots 33, 36 in the carrier 6 and support 7. When the latch holding the lens support in retracted position is released, spring 12 acting on bar 14 causes the flaps 2, 3 to open and the lens support to move outwards. Spring 12 is so formed that it exerts greatest force at the beginning of the movement to overcome the opposing action of springs 24, 25, and a smaller force towards the end of the movement, when springs 24, 25 are assisting the outward movement of the lens support 7. Springs 24, 25 are so formed as to exert a substantially constant force throughout the action. The movement stops when shoulders 41, 42 formed on support 7 abut the turned-over ends 15, 16 of bars 13, 14. The springs hold the lens support rigidly in position until the lens is retracted by pressing down the flaps 2, 3 with the hand. The parts are so arranged that the effects of wear at various points are self-compensating.